1. Field of the Invention
The present invention relates to catheters that effect heat exchange using a bundle of multiple hollow fibers.
2. Description of the Related Art
In warm blooded creatures, temperature regulation is one of the most important functions of the body. Despite the known importance of properly maintaining body temperature, scientists have discovered certain beneficial effects of artificially inducing a hypothermic state. For instance, cooling the body can help regulate vital functions during surgery by lowering the metabolism. With stroke, trauma, and other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. Also, induced hypothermia inhibits the release of damaging neurotransmitters, inhibits calcium mediated effects, inhibits brain edema, and lowers intra cranial pressure. Regardless of the particular mechanism, the present invention understands that fevers degrade the outcomes for patients suffering from brain trauma or ischemic, and moreover that hypothermia improves the outcomes for such patients.
Hypothermia may be induced locally or systemically. With local hypothermia, physicians focus their cooling efforts on a particular organ, limb, anatomical system, or other region of the body. With systemic hypothermia, doctors universally lower body temperature without particular attention to any body part.
Under one technique for inducing systemic hypothermia, physicians cool the patient""s entire body by packing it in ice. Although this technique has been used with some success, some physicians may find it cumbersome, and particularly time consuming. Also, it is difficult to precisely control body temperature with ice packing. As a result, the patient""s body temperature overshoots and undershoots the optimal temperature, requiring physicians to add or remove ice. Furthermore, there is some danger of injuring the skin, which is necessarily cooled more than any other body part.
In another approach to systemic hypothermia, the patient is covered with a cooling blanket, such as an inflatable air- or water-filled cushion. Beneficially, cooling blankets offer improved temperature control because physicians can precisely regulate the temperature of the inflation medium. Nonetheless, some delay is still inherent, first for a cooling element to change the temperature of the cooling medium, and then for the temperature adjusted cooling medium to cool the desired body part. This delay is even longer if the targeted body part is an internal organ, since the most effective cooling is only applied to the skin, and takes some time to successively cool deeper and deeper layers within the body.
The present invention recognizes that a better approach to inducing hypothermia is by circulating a cooling fluid through a cooling catheter placed inside a patient""s body. The catheter may be inserted into veins, arteries, cavities, or other internal regions of the body. The present assignee has pioneered a number of different cooling catheters and techniques in this area. Several different examples are shown in the parent ""813 application, which is hereby incorporated into the present application by reference.
Advantageously, cooling catheters are convenient to use, and enable doctors to accurately control the temperature of a targeted region. In this respect, cooling catheters constitute a significant advance. Nonetheless, the performance, efficiency, safety, and reliability of these catheters can be improved. One area of possible improvement concerns the prevention of blood clots, which can arise any time a foreign object is inserted into the bloodstream.
Broadly, the present invention concerns a catheter with multiple hollow fibers that carry a coolant fluid, where one or more fiber spreading features are employed to improve heat exchange with body fluids surrounding the catheter, as well as other benefits. Catheters constructed according to this invention generally include a length of outer tube surrounding an inner tube. The inner tube conveys fluids in one direction, whereas the passageway between the inner and outer tube conveys fluids in the opposite direction. The inner and outer tubes have proximal and distal ends. The tubes"" proximal ends are open to permit introduction (or withdrawal) of a heating or cooling fluid into the inner tube and withdrawal (introduction) of the fluid from the passageway between the inner and outer tubes. At the distal end of the tubes, a proximal fluid transfer housing is attached to multiple hollow heat exchange fibers.
One embodiment is called xe2x80x9cbound tip,xe2x80x9d because the fibers are bound together at the catheter""s distal tip. In this embodiment; the fibers continue from the proximal fluid transfer housing to a distal fluid transfer housing, attached to a reservoir. The proximal fluid transfer housing forms a sealed fluid path between the fibers and the passageway. The distal fluid transfer housing forms a sealed fluid path between the opposite ends of the fibers and the fluid reservoir and the inner tube. Fluid starts a continuous path by flowing from the inner tube""s proximal end toward its distal end. The proximal fluid transfer housing redirects fluid into the hollow fibers, where the fluid flows until it reaches the distal fluid transfer housing. The distal fluid transfer housing directs fluid into the reservoir, and then into the return passageway between the inner and outer tubes to complete the path. It is to be understood that, in a different embodiment, fluid could flow in the opposite direction as well.
A different embodiment is called xe2x80x9cfree tipxe2x80x9d because the fibers are not bound at the catheter""s tip. This embodiment eliminates the distal fluid transfer housing and reservoir. Here, each hollow fiber incorporates an outflowing lumen and a return lumen. In this embodiment, the proximal fluid transfer housing not only directs fluid into the outflowing lumens, but also guides fluid from the return lumens into the passageway between the inner and outer tubes.
In a different xe2x80x9cfree tipxe2x80x9d embodiment, the distal fluid transfer housing and reservoir are also omitted. However, each hollow fiber extends outward from the proximal fluid transfer housing and returns back again, forming a loop. Thus, the proximal fluid transfer housing not only directs fluid into one end of each hollow fiber, but also guides fluid from the opposite end of each fiber into the passageway between the inner and outer tubes.
In each of the foregoing embodiments, the invention includes actuating structure to spread the fibers under certain conditions. The actuating structure may include, for example, an elastic bowing built into the fibers to automatically curve them outward from the inner tube when there is insufficient fiber straightening pressure on the fibers. Alternatively, the fibers may be formed with shape memory, causing them to adopt a predetermined shape in response to certain temperature conditions. In another example, some or all of the fibers are pre-shaped to form spirals of predetermined amplitude and phase. In still another embodiment, the actuating structure may be provided by a spreading member coupled to a retraction line that runs within the outer tube from its distal end to its proximal end; withdrawal of the retraction line pulls the spreading member toward the common proximal ends of the fibers thereby moving the fibers apart.
The invention may be implemented in various forms, such as an apparatus or a method. An example of the apparatus is a multifiber heat exchange catheter, with various fiber spreading features. Examples of the method aspect of this invention include techniques for using or manufacturing a multifiber heat exchange catheter, etc.
The invention affords its users with a number of distinct advantages. Chiefly, by spreading the heating/cooling fibers the invention helps prevent clotting of blood or other body fluids that surround the catheter. In addition, with more widely distributed fibers, the catheter of this invention can cool the nearby tissue more efficiently. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.